For the applications of wireless communication and the need of communication bandwidth, along with the miniaturization of the 3C products, antenna devices disposed on the electronic products require not only minimizing the size, but also sustaining the efficacy of broadband. Taking the IEEE802.11 standard for example, the transmission scope of an antenna has to have sufficient bandwidth to realize the specification of the main band of 5 GHz.
Please refer to FIG. 1, which shows a traditional split ring resonator (SRR) device 100, which is disposed on a multi-layered printed circuit board. FIG. 1 shows three conductive layers relevant to the SRR device 100 in the printed circuit board, and a dielectric layer (not shown) is disposed between two adjacent conductive layers of the multi-layered printed circuit board. In FIG. 1, a top conductive layer 110 includes a gap 112 and a cavity 113 connected to the outer edge of the top conductive layer 110 through the gap 112. A plurality of grounding points 116, each of which corresponding to a plurality of connecting points 136 at the ground sheet 130 on the lower layer, are disposed around the cavity 113. Each pair of the ground point 116 and the connecting point 136 is correspondingly connected by a through hole (via) fully plated with metal. The ground sheet 130 also includes a gap 132 and a cavity 134. The conductive layer in the middle includes a feeding portion 125 which can transmit electronic signals (not shown) through a conducting line 127.
The traditional SRR antennas meet the requirements of miniaturization, but are hard to provide sufficient bandwidth, which causes the necessary communication efficacy in the application at the main frequency band of 5 GHz cannot be realized. In addition, the traditional SRR antenna device 100 as shown in FIG. 1 inevitably needs to use through holes for transmitting the antenna signals received from the feeding portion 125 at the middle layer, which would end up with unwanted signal loss because most of the functional elements are located on the top conductive layer 110 of the printed circuit board 100 according to the concepts of typical circuit board design. In order to overcome the drawbacks set forth above in the prior art, a new SRR antenna structure is required.